Oilfield wells and wellheads have a generally common configuration with nested cylindrical members. Installation of the members progresses from outer larger diameter members to inner smaller diameter members that are hung or landed on inwardly projecting portions of the surrounding outer members. The upper portions of the cylindrical members, or hangars, are generally of a more substantial annular thickness than the rest of the cylindrical member that suspends from it.
At the production stage of a well, production tubing extends down to the production zone, from where, due to differential pressure in the reservoir, oil or other hydrocarbons flow up the production tubing providing there is no mechanical barrier or blockage. However, some reservoirs do not have a high enough pressure to produce naturally and some form of artificial lift is required.
One way of providing lift is by an electrical submersible pump (ESP) installed at the bottom of the production tubing to pump the oil up the tubing. Heaters and signal paths for control equipment may also be provided. The power and signal lines for these functions need to run with the production tubing down to the reservoir.
In many applications, electrical connections are made through the top of the tubing hangar. However, space is limited, and while top entry connection and other systems, can be satisfactory for signal paths where the power requirements are generally well below 220 Watts and the cables are relatively small and compact, there is a problem in routing the larger cables required for the substantial power requirements of equipment such as electrical submersible pumps which may require over 1 KW, often 5 KW or more For example it may require the production bore to be off-centre, which has serious operational implications in ensuring equipment is correctly aligned. Furthermore, the blow out preventer has to be removed for access to the top of the tubing hangar. The tubing hangar then provides the only barrier, which causes a safety problem if the well is live.
As with any well application, pressure sealing and access without having to shut off production are required or desirable.
On way of overcoming spatial problems of top entry is to provide connections via radial penetrations. However, these require that the connector bridge the annulus between concentric members and thus the connection has to be breakable in order to allow relative vertical movement of the concentric members.
U.S. Pat. No. 6,200,152 shows electrical power and signal connections using a radial penetration to avoid problems of connection via the top of the tubing hangar. A horizontal penetration passes through concentrically disposed casings, the inner casing being a tubing hangar and the outer casing a spool body. Seals are provided between the spool body and tubing hangar to enable formation of a sealed enclosure extending from a connector portion in the wall of the tubing hangar to a shuttle housing mounted externally of the spool body. A shuttle is reciprocable in the enclosure from a position within the spool body into contact with the connector portion in order to make electrical contact. It is necessary for the cable to be able to move to allow such shuttle movement. For signal cables a loose flexible coil of cable that can expand is used, but this has been considered not possible for substantial electrical power cables, and a sliding contact on a fixed power core is used instead.
Provision of a sliding contact is complex and it is generally desirable to have fixed contacts for electrical power connections as well as for electrical signal connections.
Problems may also arise in providing optical fibre couplings in that these are sensitive to bend radius and so loose coils are not always satisfactory.